Causes of infection with Lassa fever. Symptoms, treatment and diagnosis

Lassa fever is a disease,related to the group of hemorrhagic viral infections. As a result, the kidneys are affected, the liver is destroyed, and an extensive fever develops. The disease is characterized by acute capillary toxicosis, when together with skin integuments surface vessels are damaged, their permeability sharply increases. A very life-threatening disease, lethal outcome is observed in 40% of cases. Every year, half a million people suffer from Lassa fever. The disease lasts for two weeks, the woman's fever is especially severe in the second half of pregnancy, in this case the death rate is about 80%.

Geographic areas of disease spread

In 1969, Nigerian scientists definefever among residents of the town of Lassa, the disease is being explored by nurses and nurses. Of the first five cases, three led to the death of patients. Microbiologists reveal a pathogen in a year. Fever of Lassa by this time covers countries in West Africa, such as: Guinea, Mali, Nigeria, Senegal, etc. Do not lag behind in terms of the epidemiological threshold and the Central parts of the African continent. Sometimes foci occur in European countries, Israel, the United States, Japan, where the causative agent of the virus is borne by traveling citizens.

Description of the causative agent of fever

The causative agent of the Lassa fever isan RNA-genomic viral family representative that does not have DNA, and genetic information is encoded in one or two RNA strands. The structure coincides with the construction of the virus of Bolivian and Argentinean fever, the causative agent of chorio meningitis. The diameter of the viral virion is only 80-160 nm, it is enclosed in a round lipid shell, the surface of which is covered with villi. A microscopic examination reveals a dozen ribosomes inside the virus particle, which are dense small granules.

Due to the presence of internal particles similar tograins, the virus gets the name Arenavirus from the family Arenaviridae (in Latin arenaceus means sandy). Over the past decade, scientists have identified four subgroups that are Lassa fever and are spreading in various areas of Africa. The resistance of the virus to changes in the surrounding space is that its ability to live when it enters the blood or the secrets of the body does not disappear for a long time. To reduce its activity, chloroform and ether are used.

Sources and carriers of the virus

The vectors of the virus are the many-neckedrats of the African continent, a species of Mastomys natalensis. In epidemiological hazardous areas, the number of infected individuals is 14-18% of the total number of rats, and the infected rodent carries the virus for life, sometimes without manifesting symptoms of the disease. The source of infection is also a sick person, all the fluids of which are contagious to others.

The conditions of infection with the Lassa fever aretransmission of infection through the air with drops of liquid during coughing, sneezing, breathing. Infection is found in feces and urine of rats that can get on food and human skin. Infection in infected areas occurs by inhalation of air with sprayed smallest animal excrements, using moisture from a virus-infested source of water and insufficiently digested meat of rats, commonly consumed in food.

Between them, rodents transmit the virus on contact,drinking, feeding, breeding. From the patient another person becomes infected by contact methods and sexually. A pregnant mother transmits the virus to the baby's body. The personnel of the infectious diseases clinic pick up the disease during procedures with blood and surgical intervention, autopsy, and maintenance of patients with severe catarrhal manifestations. In the blood of all patients who have had the disease, Lassa fever leaves antibodies that persist up to 7 years, which can be detected in a laboratory study.

Epidemiological situation

The disease is classified as focal viralfever. The greatest risk is to residents of western Africa. Infection is equally likely in both the village and in the city, due to the large population of tadpoles. More than half of the cases end in death.

The emergence of immunity to repetitivethe disease is poorly understood, but such cases of infection are sometimes found, while the repeated treatment and prevention of Lassa fever does not require significant effort, the disease runs in easily. Almost in all regions of Africa, infection is established year round, but the largest outbreaks occur in the cold season, when hordes of rats move closer to people's homes.

Cases of the movement of the virus to the European countriescontinents take place, but in order to prevent this spread, all those with fever are subject to strict international accounting. Men and women are equally exposed to the risk of infection. The virus is most intensively spread in places with poor sanitary conditions, densely populated areas of the poor.

Pathogenesis of the disease

Mucous membranes of the human body area kind of gateway for the infection to enter the body. The virus for the passage of the incubation period is localized in the lymph nodes, at the end of the stage there comes an acute febrile period with the spread of particles across all the systems of the body. Cells of vital organs containing the virus take on the destructive effect of cytotoxic lymphocytes, Lassa fever occurs. Symptoms and treatment of the disease are of increasing interest among specialists. In the course of the disease, necrosis of the liver and kidneys, destruction of the spleen and cardiac muscle develops.

The severity of the course of the disease depends on the immunityorganism, therefore the lethal outcome is predetermined by the violation of cellular reactions. When a feverish period of illness occurs, the formation of antibodies for the destruction of viruses is suspended and carries a delayed flow - so is the Lassa fever. Photo of the patient is presented below.

Symptoms of Lossa Disease

The incubation period lasts from a week to three, then begins an acute period of the disease, accompanied by characteristic symptoms:

• fever begins with a slight increase in body temperature;
• there is a general malaise, a feeling of weakness;
• there are myalgias, pain in the larynx when swallowing;
• eyes are affected by conjunctivitis;
• with an increase in body temperature to chill, general weakness increases;
• severe pain occurs in the back, abdomen, and chest;
• sometimes there is nausea, diarrhea, convulsions;
• a strong cough becomes vomiting;
• the visual perception of the surrounding space is disturbed.

Patient examination

Always on examination there is swelling of the neck andface, thoracic region, hemorrhagic effects occur in different areas, with palpation there is a large increase in lymph nodes. Examination of the larynx reveals ulcers, the mucosa is characterized by the appearance of white spots, precursors of subsequent ulcers, which gives Lassa fever. Symptoms in the examination of the heart are manifested in subdued tones, pronounced bradycardia and an increase or decrease in blood pressure. With the further course of the disease, myocarditis develops, and the bradycardia is replaced by tachycardia.

The examination on suspicion of the disease revealson the skin of the patient numerous hemorrhages, in addition to them, there are spots, papules, roseola, sometimes the rash in nature resembles the manifestation of measles. The heart is enlarged, the patient is disturbed by shortness of breath, cough, wheezing in the lungs of a wet or dry nature. The internal areas of the peritoneum make themselves felt by pain, rumbling in the abdomen, diarrhea. At inspection the liver is increased. Nervous system disorders are also manifested by Lassa fever. Epidemiology notes cases of loss of consciousness, hearing, noise in the ears, there is complete or partial baldness of the head.

Laboratory blood tests revealleukopenia, then leukocytosis, with the leukocyte formula shifting to the left, characterized by an increased platelet count and a decrease in the level of prothrombin, an increase in ESR to 50-80 mm / h. Clotting of blood decreases, an increase in the prothrombin period is observed. Insufficiency of the kidneys makes itself felt by the high content of urea in the blood, the urine of the patient reveals proteinuria and cylindruria. Urine contains leukocytes, erythrocytes, impurities of protein, granular cylinders.

Since Lassa fever refers to focalnatural diseases, then if a virus is suspected, an epidemiological anamnesis is carried out, and the prerequisites for the manifestation of the disease are identified because of the patient's stay in the contaminated area. As instrumental studies, X-ray, FDSG, ultrasound, MRI of disturbed organs and body systems are used. On the definition of the disease, patients consult a pulmonologist, cardiologist, neuropathologist, gastroenterologist.

Severe course and complications

In 37-52% of cases, the severity of the disease leads tosevere lung lesions (pneumonia of different severity), heart (myocarditis), liver (cirrhosis), kidney (insufficiency). The severe swelling of the pleural areas of the body is manifested by the Lassa fever. Epidemiology, clinic, prevention do not always give positive predictions and have a healing effect. More than half of the cases predict the death of the patient after two weeks from the onset of the illness. The favorable course of the disease lasts from 3 weeks, then the temperature begins to decrease. Recovery is slow, symptoms re-appear, relapses occur from time to time.

Differentiation of the diagnosis with other diseases

For many symptoms, the manifestation of the disease is similarwith hemorrhagic fevers of other types. Typhus fever, Dengue fever, yellow fever, Kyasanur forest disease, West Nile fever, Chikungunya, malaria of the tropics, scarlet fever, meningitis resembles Lassa fever. Marburg, Ebola also on the grounds have much in common and should be excluded from suspected diseases.

Malaria is similar to Lassa's symptoms in thatBoth diseases show high body temperature, headaches, yellowing of the skin. The difference is that malaria is not characterized by the appearance of necrotic ulcers in the larynx and a large enlargement of the lymph nodes, hemorrhagic syndrome rarely develops. In addition, malaria is characterized by pallor of the skin, increased sweating and uneven fever, focal rashes.

Hemorrhagic fever with renal syndromecharacterized by common symptoms with Lassa's disease, manifested by headaches and muscle cramps, scleritis, conjunctivitis, oliguria. But HFRS does not cause a person multiple vomiting, ulcerative pharyngitis and diarrhea. In contrast to Lass disease, from the first day of the course of this disease, dry mouth, severe thirst and severe muscle weakness occur.

For leptospirosis, there are similar signs ina feverish state, headaches, myalgia, conjunctivitis, scleritis, oliguria. But the absence of necrotic ulcers in leptospirosis in the mouth distinguishes him from the disease Lassa fever. With leptospirosis there is no coughing, diarrhea, vomiting, there are no chest pains, it is not revealed in laboratory studies of leukopenia, bradycardia. Absolutely different signs have a fever of Lassa. The photos of the affected people are shown below.

Acute viral fever Marburg passes withsevere symptoms, there are symptoms similar to Lass disease. It is characterized by a high degree of death, development of a febrile state, hemorrhagic syndrome, severe damage to internal organs and the central nervous system. The source of the infection is not exactly established, it is assumed that the virus is transmitted to humans from green monkeys by drip or air, as well as by contact with the animal.

Treatment methods

All patients with suspected infectionare subject to mandatory admission to special clinics. When maintaining the patient on treatment, a strict isolation regime is observed without the slightest violation. The horizontal bed position is prescribed, the load is excluded, the treatment is aimed at eliminating the emerging symptoms of the disease. In the first weeks, the causes are determined, and the treatment of Lassa fever primarily consists in the use of plasma convalescent. This is effective only at the onset of the disease, since the use of the drug for prolonged fever causes, in some cases, worsening of the disease and the development of complications.

The complication of the disease is treated with strongantibiotics and glucocorticoids. In the modern medical pharmaceutical business, new etiotropic drugs and vaccines have been developed. Effective today is the use in the treatment of drugs virazol, ribamidil, ribavirin. They are taken orally in the initial stage of the disease, in the amount of 1000 units per day. The reception does not stop for 10 days. Intravenously, it is enough to administer the medication within 4 days, which helps to improve the course of the disease, and to reduce the death rate.

Prevention of disease

Too much loss of lifefor a lassa fever. Preventive maintenance of disease is of paramount importance in epidemiological dangerous areas. To prevent the virus from penetrating human habitation, it is necessary to stop access to it of tadpole rats and rodents of other species. Usually food products and wells of fresh drinking water are carefully concealed in order to exclude urine and excrement of rodents from entering them. As a prophylactic treatment, rats are etched everywhere with subsequent burning of carcasses.

A great preventive value is given toincrease the standard of living of the indigenous African population, improve the quality of nutrition for the emergence of sufficient immune protection of the body. Conducted conversations and lectures to improve the cultural and community level, explains the need to comply with individual health standards for each person.

Doctors and other medical personnel are infectiousclinics are necessarily provided with the necessary means of personal prevention, such as gloves and masks for the care of patients. The training of local and sent to the epidemiological dangerous area of ​​doctors for the correct and safe evacuation and antiepidemic regime.

Carrying out of actions in the center of occurrence of epidemic

Systematized quarantine actionsnecessarily take place, if in any area there is a fever of Lassa. Anti-epidemic measures are implemented urgently without delay. They are aimed at organizing a strict quarantine with complete isolation of patients in infectious boxes, warning the local population about the onset of the epidemic. All involved personnel are required to wear anti-plague suits and personal protective equipment.

Obligatory is the hospitalization of persons,suspected of contact with the diseased, the burning of material things that are not of material value and objects of everyday life of the big and contact people, the burning in the crematorium of the bodies of the deceased from the illness, the disinfection in the rooms and houses. Individuals arriving in the "clean" areas from the epidemic are isolated to the inpatient facilities if there is the slightest suspicion of the onset of the disease.

In conclusion, it should be noted that the deadlythe fever recedes, if security measures are strictly implemented, effective measures are taken to reduce the risk of the disease, treatment is started in a timely manner.